1. Field of the Invention
The present invention relates to head-lamps mounted on an automobile or the like, and more specifically to a construction of an adjuster for matching an illuminating direction with a vehicle body.
2. Description of the Prior Art
FIG. 4 shows a conventional head-lamp 51 of this kind. A pivot portion 52 and an adjusting screw portion 53 are provided on the head-lamp 51 to form an adjuster construction, in which when it is mounted on an automobile (not shown), an illuminating direction can be corrected. Normally, as the pivot portion 52, a ball joint comprising a shaft surface 52a in the form of a spherical surface and a carrying surface 52 in the form of a spherical concave surface is used. The adjusting screw portion 53 is provided with an adjusting screw 53a, a screw head receiving portion 53b and a nut 53c. The adjusting screw 53a is rotated to vary a spacing between the screw receiving portion 53b and the nut 53c to correct an illuminating direction of the head lamp 51. Since the head-lamp 51 is rotated about the pivot portion 52, a ball joint having a construction similar to said pivot portion 52 is used for either said screw head receiving portion 53b or the nut 53c (an example of the screw head receiving portion 53b is shown) to cope therewith to prevent an occurrence of variation in the rotational torque when stress applied to the adjusting screw 53a is corrected.
However, it is general in terms of hardness or ease in molding, in the conventional ball joint the shaft surface 52a is principally formed from a metal member whereas the carrying surface 52b is formed from a resin member. Therefore, the external surface is surrounded by a member having a large coefficient of thermal expansion, and a surplus fastening force is produced due to a variation in environmental temperature, resulting in an occurrence of a rotational torque of the adjusting screw 53a. There poses a problem in that for example, in an extremely cold season, correction work becomes impossible due to the aforesaid fastening force. In an extremely hot season, the rotational torque becomes extremely small, thus posing a problem in that a retentiveness of correction is lowered. These problems have been required to be solved.